1. Field of the Invention
The present invention relates to a drive-in dowel including an inner sleeve having load application means, preferably, in a form of an inner thread, and a cone-shaped widening section formed at a front, in a setting direction, end of the inner sleeve and an outer sleeve arranged coaxially with the inner sleeve, and having, in a front, in the setting direction region thereof, a plurality of expansion tabs separated from each other by longitudinal slots and radially expandable upon the outer sleeve being impact driven over the cone-shaped widening section of the inner sleeve.
2. Description of the Prior Art
Anchoring of conventional drive-in dowels is based primarily on an expansion principle. The used percussion or impact-driven expansion dowels are primarily formed of two parts and includes, e.g., a sleeve-shaped dowel body with a conical bore and a spreading member. In order to anchor the dowel in a prepared bore, the spreading member is percussion driven into the expandable region of the sleeve-shaped dowel. This causes expansion of the expandable region and a force-locking connection of the radially expanded expandable region of the dowel with the bore wall. However, the multi-part construction of the known dowel can cause several problems. E.g., the spreading member can be incorrectly inserted in the dowel body bore. Also, the spreading member can fall out of the bore and become lost. Further, with the spreading member being arranged and held outside of the dowel body bore, it can happen that upon a miss, the spreading member becomes inclined and would wedge.
The prior art discloses also a driven-in dowel the anchoring of which in a bore of a structural component is effected by axial displacement of two concentrically arranged sleeves. Thus, U.S. Pat. No. 2,171,985 discloses a percussion driven expansion dowel formed of an inner sleeve having an inner thread and supported against a bore bottom and an expansion sleeve displaceable over the inner sleeve. In the front end region of the inner sleeve, there is provided a section conically widening in a setting direction. The expansion sleeve has a plurality of expansion tabs separated by longitudinal slots from each other. The expansion tabs expand radially upon the expansion sleeve being percussion driven over the conical section of the inner sleeve. The anchoring of the expansion dowel is effected as a result of application of an expansion force which is imparted by the radially expanded expansion tabs to the bore wall.
The anchoring in accordance with expansion principle requires application of a high expansion force. This leads to large distances between axes and edges of formed attachment points. Because these distances not always can be maintained, there are provided systems, which are based on expandable drive-in dowels and which are anchored in bores of structural components as a result of a form-locking connection. Such systems make use of undercuts which are usually formed in the region of a bore bottom. The anchoring is effected with expansion tabs which are provided on a sleeve-shaped dowel body and which expand radially into an undercut, forming a form-locking connection. In many cases, in which form-lockingly anchoring undercut systems are used, it is often necessary to form an undercut at an exactly predetermined depth in a separate step with a special tool. Only after an undercut is formed in a bore wall, an undercut dowel can be inserted in the bore and form-lockingly anchored by percussion driving the expansion tabs over the sleeve cone section.
Also known are undercut self-cutting systems with which an undercut-forming dowel when being percussion driven into a bore, automatically forms an undercut by tangentially shaving the wall material. The known undercut self-cutting systems permit to obtain, within acceptable time limits, a form-locking connection. However, such undercut self-cutting systems can be used in small load application regions, with tensile loads less than 20 kN. As an alternative to the undercut self-cutting systems, undercut pressing dowels are used which represent an intermediate stage between percussion driven expansion dowels and undercut self-cutting dowel. With the undercut pressing dowels, the expansion elements, upon their radial expansion, are pressed into a form-locking engagement with a bore wall. The undercut pressing dowels form a form-locking engagement by volumetric displacement or repression. However, for an impressed depth greater than 1 mm, the necessary pressure force disproportionally increases. This is because the force increases at least in a square degree in comparison with a displaced volume. This leads to a destruction of the bore wall material and to degradation of the initial rigidity of the undercut pressing dowel. At a pressed-in depth of about 5 mm, cracks in concrete can be formed which substantially reduces the load bearing capability of a dowel.
Accordingly, an object of the present invention is to eliminate or at least substantially reduce the drawback of the prior art drive-in dowels. Another object of the present invention is to provide a drive-in dowel which can be easily form-lockingly anchored in a structural component. Expensive undercut-forming special tools should be eliminated. The energy consumption necessary for effecting anchoring should be relatively small and should be obtainable with axial impacts with a hammer. Further, forming undercuts with a depth of 5 mm and greater should be possible, without a disproportional increase of the energy consumption with increase of the undercut depth. The drive-in dowel should not form cracks or crevices in structural component and should have a secondary expansion capability. The drive-in dowel should also have a simple construction and be cost-effective. The drive-in dowel should further provide a user with an indication of when the anchoring has been obtained.